This invention relates to electrical connecting devices, and particularly to an electrical adapter plug which may be inserted into the sockets or receptacles of automotive cigarette lighter assemblies so that various low voltage loads may be operated by the electrical system of the vehicle.
In recent years, a great variety of electrical appliances have become available for operation by the low voltage, direct-current power of the electrical systems of cars, power boats, and campers. The appliance is generally interconnected to the electrical system of the vehicle by use of an adapter plug or connector which is inserted into the cigarette lighter socket or receptacle. Electrical appliances and accessories which can be operated from a vehicle electrical system vary widely and include portable television sets, tape recorders, trouble lights, window defrosters, electric shavers, electric toothbrushes, can openers, food mixers, and the like.
Such prior art devices useful for electrical connection with cigarette lighter receptacles include Focosi U.S. Pat. No. 2,954,544, Schwartz U.S. Pat. No. 3,099,505, Busch et al U.S. Pat. No. 3,377,610 and Busch U.S. Pat. No. 3,865,463.
In general, existing adapter plug designs each have one or two spring contacts mating with a receptacle sleeve. If there are two contacts, they are usually angularly spaced to project from the periphery of an adapter plug body at an angle of 180.degree.. Accordingly, the vector sum of the mechanical forces of two contacts within the sleeve are in-line or 180.degree. opposing and there is zero force on the body of the adapter plug to position it against the receptacle surface. Thus the adapter plug is able to pivot on the in-line contact points within the receptacle. When the adapter plug is free to pivot more, it can loosen and eventually lose electrical contact when subject to vibration or shock.
I disclosed in my U.S. Pat. No. 4,998,315 issued Jan. 29, 1991 for Electrical Adapter Plug a novel electrical adapter plug design having a pair of spaced electrical spring contacts located on the periphery of an adapter plug body. These contacts cooperate with a diametrically opposite groove in a first preferred embodiment to establish improved mating contact with the cylindrical sleeve of a cigarette lighter receptacle when the adapter plug is manually inserted into the receptacle. In particular, two negative or side contacts on the adapter plug are positioned to provide a force on the body of the adapter plug resulting in better contact engagement with the receptacle sleeve. The two spring contacts are radially positioned opposite each other at an included angle of less than 180.degree.. The resultant vector force effects a peripheral contact of the adapter plug to the receptacle sleeve (and depending upon the particular preferred embodiment employed) a stable two point and a one line or alternatively a two line engagement of the mated adapter plug and receptacle sleeve.
In a first preferred embodiment shown in my earlier application, a groove is strategically located on the periphery of the adapter plug body diametrically opposite the electrical contacts and centered on a line which represents an extension of the resultant force vector generated by the two spring contacts. The two sidewall edges, Which define the groove, make a spaced two-line contact with the receptacle sleeve.
Accordingly, the adapter plug makes contact with the sleeve of the receptacle in four areas, namely, the two lines which define the two edges of the groove and the two spring contact points. This four area mating contact between the adapter plug and its receptacle greatly improves the retention of the adapter plug in the receptacle.
Prior art adapter plug designs which are commercially available have one or two electrical spring contacts mating with the receptacle sleeve. If there are two contacts, they are 180.degree. opposing. It is noted, however, U.S. Pat. No. 2,489,037 issued Nov. 22, 1949 discloses a non-commercial adapter plug having contacts located at an included angle of 90.degree.. This patented design does not use a groove, or other equivalent means, to establish line contact with the inner wall of the receptacle.
This in-line disposition of forces enables the adapter plug to pivot on the in-line contact areas (or points) established with the receptacle. When the adapter plug is free to pivot or move, it can loosen and eventually break electrical contact when subjected to vibration or jarring.
In a second preferred embodiment shown in my earlier application, the periphery of the adapter plug body is formed with a protruding portion (the groove of the first embodiment is eliminated) diametrically opposite the electrical contacts and centered on a line which represents an extension of the resultant force vector generated by the two spring contacts. The resultant vector force effects contact of the adapter plug to the receptacle sleeve in three spaced areas, namely the two spaced spring contact points and the line of contact between the protruding portion and the receptacle sleeve.
A third preferred embodiment is also described in my earlier application which features a flat adapter-plug body portion (in lieu of a groove) to define two line contact areas which function similar to the groove edges.